This invention relates generally to floating cranes with a derricking jib and concerns more specifically the provision of an auxiliary jib in such a crane.
In conventional floating cranes with a derricking jib it is the practice for the purpose of increasing outreach and luffing height to fit a supplementary top mounting jib. Top mounting jibs are mounted on laterally projecting hinge pins at the top or head of the main jib. In the case of hitherto conventional top mounting jibs which are about 20 meters in length the crane is capable of picking up the supplementary jib from the horizontal without assistance. If the top mounting jib is of greater length, external assistance is needed to lift the additional weight.
For the assembly of special constructions, such as offshore rigs, great luffing heights and load lifting capacities are required. These requirements cannot be satisfactorily met by conventional supplementary jibs mounted at the top of the main jib. The lengths of rope on the derrick winch needed for erecting such systems would far exceed the rope lengths needed for luffing the loads. Moreover, the design weight of the main jib for taking up the greater loads would also have to be higher.